The present invention relates to a thermal overload relay for change-over of a contact upon detection of an overcurrent.
Japanese Examined Patent Publication No. H7-001665 (Patent Document 1), for example, discloses a thermal overload relay operated by detecting an overcurrent running in the main circuit.
The thermal overload relay of Patent Document 1 is described referring to FIG. 4.
This thermal overload relay comprises, in an insulator case 1 made of a resin mould, main bimetals 2 inserted in three phase electric circuit and wound with heaters 2a, a shifter 3 linked to free ends of the main bimetals 2 and movably supported on the insulator case 1, a switching mechanism 4 disposed in the insulator case 1 allowing linking to an end of the shifter 3, and a contact reversing mechanism 5 to changeover contacts by operation of the switching mechanism 4.
The switching mechanism 4 comprises a temperature compensation bimetal 7 linked to one end of the shifter 3, a release lever 8 fixed to the other end of the temperature compensation bimetal 7, and an adjusting cam 12 connected to the release lever 8 through a swinging pin 9 projecting at the lower end of the adjusting mechanism and abutting on the circumferential surface of an eccentric cam 11a of an adjusting dial 11, disposed rotatably in the insulator case 1 at the upper end of the adjusting cam 12. A rotation angle of the release lever 8 is set by varying an abutting position of the adjusting cam 12 on the circumferential surface of the eccentric cam 11a of the adjusting dial 11 through adjustment of the adjusting dial 11, thereby slightly rotating the adjusting cam 12 around a support shaft 13.
The contact reversing mechanism 5 comprises a reversing spring 14 fixed at its lower end to the release lever 8 and extending upwards, a slider 17 linking to the tip of the reversing spring 14 and moving a normally opened side movable contact piece 15b and a normally closed side movable contact piece 16a, and a reset bar 18 to manually move the slider 17 to a normal position. The reversing spring 14 is a member having a punched window (not shown in the figure) formed by punching a thin spring material, and a curved surface with a disc spring shape around the punched window. The reversing spring 14 is convexly curved towards right hand side in a normal state shown in FIG. 4.
When the bimetal 2 bends with the heat generated by the heater 2a due to an overcurrent in the above-described structure, the shifter 3 shifts to the direction indicated by the arrow P in FIG. 4 caused by displacement of the free end of the main bimetal 2. The Shift of the shifter 3 pushes a free end of the temperature compensation bimetal 7 and rotates the release lever 8 counterclockwise around the swinging pin 9.
With progression of the counterclockwise rotation of the release lever 8, the reversing spring 14 deforms bending convexly towards the left hand side. The deformation of the reversing spring 14 moves the slider 17, which is linked to the tip of the reversing spring 14, so as to change the normally opened side movable contact piece 15b and the normally opened side fixed contact piece 15a into a closed state and to change the normally closed side movable contact piece 16a and the normally closed side fixed contact piece 16b into an opened state.
Based on the information of the closed state of the normally opened side movable contact piece 15b and the normally opened side fixed contact piece 15a, and the information of the opened state of the normally closed side movable contact piece 16a and the normally closed side fixed contact piece 16b conducted by the reversing action of the switching mechanism 4, an electromagnetic contactor (not shown in the figures), for example, connected in the main circuit is opened to interrupt the overcurrent.
Meanwhile, in the contact reversing mechanism 5 of the conventional thermal overload relay described above, the slider 17 for change over of the normally opened contact (the normally opened side movable contact piece 15b and the normally opened side fixed contact piece 15a) and the normally closed contact (normally closed side movable contact piece 16a and the normally closed side fixed contact piece 16b) is placed flatly in the region over the main bimetals 2 in the insulator case 1. Moreover, the reversing spring 14 for moving the slider 17 is placed in a region different from the region for placing the slider 17. Therefore, a large space is required in, the insulator case 1, which is a problem in that it hinders a size reduction of a thermal overload relay.
In view of the above-described unsolved problems in the conventional technology examples, it is an object of the present invention to provide a thermal overload relay in which a space for placing a normally opened contact and a normally closed contact is reduced in the case, thereby minimizing the size of a thermal overload relay.
Further objects and advantages of the invention will be apparent from the following description of the invention.